Useful "One-liners"
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Useful `awk' programs are often short, just a line or two. Here is a
collection of useful, short programs to get you started. Some of these
programs contain constructs that haven't been covered yet. The
description of the program will give you a good idea of what is going
on, but please read the rest of the manual to become an `awk' expert!
Since you are reading this in Info, each line of the example code is
enclosed in quotes, to represent text that you would type literally.
The examples themselves represent shell commands that use single quotes
to keep the shell from interpreting the contents of the program. When
reading the examples, focus on the text between the open and close
quotes.
`awk '{ if (NF > max) max = NF }'
` END { print max }''
This program prints the maximum number of fields on any input line.
`awk 'length($0) > 80''
This program prints every line longer than 80 characters. The sole
rule has a relational expression as its pattern, and has no action
(so the default action, printing the record, is used).
`awk 'NF > 0''
This program prints every line that has at least one field. This
is an easy way to delete blank lines from a file (or rather, to
create a new file similar to the old file but from which the blank
lines have been deleted).
`awk '{ if (NF > 0) print }''
This program also prints every line that has at least one field.
Here we allow the rule to match every line, then decide in the
action whether to print.
`awk 'BEGIN { for (i = 1; i <= 7; i++)'
` print int(101 * rand()) }''
This program prints 7 random numbers from 0 to 100, inclusive.
`ls -l FILES | awk '{ x += $4 } ; END { print "total bytes: " x }''
This program prints the total number of bytes used by FILES.
`expand FILE | awk '{ if (x < length()) x = length() }'
` END { print "maximum line length is " x }''
This program prints the maximum line length of FILE. The input is
piped through the `expand' program to change tabs into spaces, so
the widths compared are actually the right-margin columns.
`awk 'BEGIN { FS = ":" }'
` { print $1 | "sort" }' /etc/passwd'
This program prints a sorted list of the login names of all users.
`awk '{ nlines++ }'
` END { print nlines }''
This programs counts lines in a file.
`awk 'END { print NR }''
This program also counts lines in a file, but lets `awk' do the
work.
`awk '{ print NR, $0 }''
This program adds line numbers to all its input files, similar to
`cat -n'.